Calcium is the single most important messenger molecule in mammalian cells. Fluctuations in its concentration control a myriad of processes from gene expression to wound healing. The goal of this proposal is the chemical synthesis of photochemically based probes that will be used to control calcium concentration in living animals. New laser and microscope technologies now permit the imaging of structures as small single synapses in vivo. We wish to use this technology (the two-photon microscope) to be more than passive observers of cell function. We propose to make chemical probes that will allow us to actively intervene in the calcium dynamics of individual cells in vivo. To do this we will take advantage of a new chromophore we have recently made (called "NDBF"), that is uniquely sensitive to two-photon excitation. We will develop functionally inert (or "caged") derivatives of IPS or calcium receptor agonists that are photochemically liberated by two-photon photolysis. These new probes will be used in collaboration with other scientists to study how basic calcium-regulated processes encode memory at the level of single synapses. They will also be used, in concert with two-photon imaging of calcium, to probe the dynamics of calcium signaling in mouse models of disease states such epilepsy and Alzheimer's, as well as during nicotine addiction. Calcium signaling is significantly perturbed by these states. The photochemical probes we propose to develop will enable us to examine these changes in living animals for the first time.